Getting the pole "plumb"

Hi

I have a problem where I'm not sure if my mount pole is plumb and I believe its causing me problems.

On Western satellites I get a better signal by moving the elevation up slightly, while for Eastern satellites moving it down slightly helps.

What does this indicate about my pole? According to Bubble Level (app for Android) it is fine, but with the above I doubt the 100% accuracy of this.

Which way does the problem suggest my pole needs slightly moving?

Thanks